Python’s array module defines the array class. An object of array class is similar to the array as present in Java or C/C++. Unlike the built-in Python sequences, array is a homogenous collection of either strings, or integers, or float objects.
The array class doesn’t have any function/method to give a sorted arrangement of its elements. However, we can achieve it with one of the following approaches −
Using a sorting algorithm
Using the sort() method from List
Using the built-in sorted() function
Let’s discuss each of these methods in detail.
Sort Arrays Using a Sorting Algorithm
We implement the classical bubble sort algorithm to obtain the sorted array. To do it, we use two nested loops and swap the elements for rearranging in sorted order.
Example
Run the following code using a Python code editor −
import array as arr
a = arr.array('i',[10,5,15,4,6,20,9])for i inrange(0,len(a)):for j inrange(i+1,len(a)):if(a[i]> a[j]):
array('i', [4, 5, 6, 9, 10, 15, 20]) Sort Arrays Using sort() Method of List Even though array module doesn't have a sort() method, Python's built-in List class does have a sort method. We shall use it in the next example.
First, declare an array and obtain a list object from it, using tolist() method. Then, use the sort() method to get a sorted list. Lastly, create another array using the sorted list which will display a sorted array.
Example The following code shows how to get sorted array using the sort() method.
import array as arr
# creating array orgnlArray = arr.array('i', [10,5,15,4,6,20,9]) print("Original array:", orgnlArray) # converting to list sortedList = orgnlArray.tolist() # sorting the list sortedList.sort()
# creating array from sorted list sortedArray = arr.array('i', sortedList) print("Array after sorting:",sortedArray) The above code will display the following output −
Original array: array('i', [10, 5, 15, 4, 6, 20, 9]) Array after sorting: array('i', [4, 5, 6, 9, 10, 15, 20]) Sort Arrays Using sorted() Method The third technique to sort an array is with the sorted() function, which is a built-in function.
The syntax of sorted() function is as follows −
sorted(iterable, reverse=False) The function returns a new list containing all items from the iterable in ascending order. Set reverse parameter to True to get a descending order of items.
The sorted() function can be used along with any iterable. Python array is an iterable as it is an indexed collection. Hence, an array can be used as a parameter to sorted() function.
Example In this example, we will see the use of sorted() method in sorting an array.
import array as arr a = arr.array('i', [4, 5, 6, 9, 10, 15, 20]) sorted(a) print(a) It will produce the following output −
Reversing an array is the operation of rearranging the array elements in the opposite order. There are various methods and approaches to reverse an array in Python including reverse() and reversed() methods.
In Python, array is not one of the built-in data types. However, Python’s standard library has array module which helps us to create a homogenous collection of string, integer or float types.
Ways to Reverse an Array in Python
To reverse an array, use the following approaches −
Using slicing operation
Using reverse() method
Using reversed() method
Using for loop
Using slicing operation
Slicing operation is the process of extracting a part of array within the specified indices. In Python, if we use the slice operation in the form [::-1] then, it will display a new array by reversing the original one.
In this process, the interpreter starts from the end and stepping backwards by 1 until it reaches the beginning of the array. As a result, we get a reverse copy of original array.
Example
The below example demonstrates how to use the slicing operation to reverse an array in Python.
We can also reverse the sequence of numbers in an array using the reverse() method of list class. Here, list is a built-in type in Python.
Since reverse() is a method of list class, we cannot directly use it to reverse an array created through the Python array module. We have to first transfer the contents of an array to a list with tolist() method of array class, then we call the reverse() method and at the end, when we convert the list back to an array, we get the array with reversed order.
Example
Here, we will see the use of reverse() method in reversing an array in Python.
import array as arr
# creating an array
numericArray = arr.array('i',[10,5,15,4,6,20,9])print("Array before reversing:", numericArray)# converting the array into list
newArray = numericArray.tolist()# reversing the list
newArray.reverse()# creating a new array from reversed list
revArray = arr.array('i', newArray)print("Array after reversing:",revArray)
The reversed() method is another way to reverse elements of an array. It accepts an array as a parameter value and returns an iterator object that dispalys array elements in reverse order.
Example
In this example, we are using the reversed() method to reverse an array in Python.
import array as arr
# creating an array
numericArray = arr.array('i',[12,10,14,16,20,18])print("Array before reversing:", numericArray)# reversing the array
newArray =list(reversed(numericArray))# creating a new array from reversed list
revArray = arr.array('i', newArray)print("Array after reversing:",revArray)
On executing the above code, it will display the following output −
Array before reversing: array('i', [12, 10, 14, 16, 20, 18])
Array after reversing: array('i', [18, 20, 16, 14, 10, 12])
Using for Loop
To reverse an array using a for loop, we first traverse the elements of the original array in reverse order and then append each element to a new array.
Example
The following example shows how to reverse an array in Python using for loop.
import array as arr
a = arr.array('i',[10,5,15,4,6,20,9])
b = arr.array('i')for i inrange(len(a)-1,-1,-1):
b.append(a[i])print(a)print(b)
In Python, copying an array refers to the process of creating a new array that contains all the elements of the original array. This operation can be done using assignment operator (=) and deepcopy() method. In this chapter, we discuss how to copy an array object to another. But, before getting into the details let’s breifly discuss arrays.
Python’s built-in sequence types i.e. list, tuple, and string are indexed collection of items. However, unlike arrays in C/C++, Java etc. they are not homogenous, in the sense the elements in these types of collection may be of different types. Python’s array module helps you to create object similar to Java like arrays.
Python arrays can be of string, integer or float type. The array class constructor is used as follows −
Where, the typecode may be a character constant representing the data type.
Copy Arrays Using Assignment Operator
We can assign an array to another by using the assignment operator (=). However, such assignment doesn’t create a new array in the memory. Instead, it creates a new reference to the same array.
Example
In the following example, we are using assignment operator to copy array in Python.
import array as arr
a = arr.array('i',[110,220,330,440,550])
b = a
print("Copied array:",b)print(id(a),id(b))
Check the id() of both a and b. Same value of id confirms that simple assignment doesn’t create a copy. Since “a” and “b” refer to the same array object, any change in the array “a” will reflect in “b” too −
To create another physical copy of an array, we use another module in Python library, named copy and use deepcopy() function in the module. A deep copy constructs a new compound object and then, recursively inserts copies into it of the objects found in the original.
Example
The following example demonstrates how to copy array in Python −
import array as arr
import copy
a = arr.array('i',[110,220,330,440,550])
b = copy.deepcopy(a)print("Copied array:",b)
On executing, it will produce the following output −
Loops are used to repeatedly execute a block of code. In Python, there are two types of loops named for loop and while loop. Since the array object behaves like a sequence, you can iterate through its elements with the help of loops.
The reason for looping through arrays is to perform operations such as accessing, modifying, searching, or aggregating elements of the array.
Python for Loop with Array
The for loop is used when the number of iterations is known. If we use it with an iterable like array, the iteration continues until it has iterated over every element in the array.
Example
The below example demonstrates how to iterate over an array using the “for” loop −
import array as arr
newArray = arr.array('i',[56,42,23,85,45])for iterate in newArray:print(iterate)
The above code will produce the following result −
56
42
23
85
45
Python while Loop with Array
In while loop, the iteration continues as long as the specified condition is true. When you are using this loop with arrays, initialize a loop variable before entering the loop. This variable often represents an index for accessing elements in the array. Inside the while loop, iterate over the array elements and manually update the loop variable.
Example
The following example shows how you can loop through an array using a while loop −
import array as arr
# creating array
a = arr.array('i',[96,26,56,76,46])# checking the length
l =len(a)# loop variable
idx =0# while loopwhile idx < l:print(a[idx])# incrementing the while loop
idx+=1
On executing the above code, it will display the following output −
96
26
56
76
46
Python for Loop with Array Index
We can find the length of array with built-in len() function. Use it to create a range object to get the series of indices and then access the array elements in a for loop.
Example
The code below illustrates how to use for loop with array index.
import array as arr
a = arr.array('d',[56,42,23,85,45])
l =len(a)for x inrange(l):print(a[x])
On running the above code, it will show the below output −
Python arrays are a mutable sequence which means operation like adding new elements and removing existing elements can be performed with ease. We can remove an element from an array by specifying its value or position within the given array.
The array module defines two methods namely remove() and pop(). The remove() method removes the element by value whereas the pop() method removes array item by its position.
Python does not provide built-in support for arrays, however, we can use the array module to achieve the functionality like an array.
Remove First Occurrence
To remove the first occurrence of a given value from the array, use remove() method. This method accepts an element and removes it if the element is available in the array.
Syntax
array.remove(v)
Where, v is the value to be removed from the array.
Example
The below example shows the usage of remove() method. Here, we are removing an element from the specified array.
import array as arr
# creating array
numericArray = arr.array('i',[111,211,311,411,511])# before removing arrayprint("Before removing:", numericArray)# removing array
numericArray.remove(311)# after removing arrayprint("After removing:", numericArray)
It will produce the following output −
Before removing: array('i', [111, 211, 311, 411, 511])
After removing: array('i', [111, 211, 411, 511])
Remove Items from Specific Indices
To remove an array element from specific index, use the pop() method. This method removes an element at the specified index from the array and returns the element at ith position after removal.
Syntax
array.pop(i)
Where, i is the index for the element to be removed.
Example
In this example, we will see how to use pop() method to remove elements from an array.
import array as arr
# creating array
numericArray = arr.array('i',[111,211,311,411,511])# before removing arrayprint("Before removing:", numericArray)# removing array
numericArray.pop(3)# after removing arrayprint("After removing:", numericArray)
It will produce the following output −
Before removing: array('i', [111, 211, 311, 411, 511])
After removing: array('i', [111, 211, 311, 511])
Python array is a mutable sequence which means they can be changed or modified whenever required. However, items of same data type can be added to an array. In the similar way, you can only join two arrays of the same data type.
Python does not have built-in support for arrays, it uses array module to achieve the functionality like an array.
Adding Elements to Python Array
There are multiple ways to add elements to an array in Python −
Using append() method
Using insert() method
Using extend() method
Using append() method
To add a new element to an array, use the append() method. It accepts a single item as an argument and append it at the end of given array.
Syntax
Syntax of the append() method is as follows −
append(v)
Where,
v − new value is added at the end of the array. The new value must be of the same type as datatype argument used while declaring array object.
Example
Here, we are adding element at the end of specified array using append() method.
import array as arr
a = arr.array('i',[1,2,3])
a.append(10)print(a)
It will produce the following output −
array('i', [1, 2, 3, 10])
Using insert() method
It is possible to add a new element at the specified index using the insert() method. The array module in Python defines this method. It accepts two parameters which are index and value and returns a new array after adding the specified value.
Syntax
Syntax of this method is shown below −
insert(i, v)
Where,
i − The index at which new value is to be inserted.
v − The value to be inserted. Must be of the arraytype.
Example
The following example shows how to add array elements at specific index with the help of insert() method.
import array as arr
a = arr.array('i',[1,2,3])
a.insert(1,20)print(a)
It will produce the following output −
array('i', [1, 20, 2, 3])
Using extend() method
The extend() method belongs to Python array module. It is used to add all elements from an iterable or array of same data type.
Syntax
This method has the following syntax −
extend(x)
Where,
x − This parameter specifies an array or iterable.
Example
In this example, we are adding items from another array to the specified array.
import array as arr
a = arr.array('i',[1,2,3,4,5])
b = arr.array('i',[6,7,8,9,10])
a.extend(b)print(a)
On executing the above code, it will produce the following output −
Accessing an array items in Python refers to the process of retrieving the value stored at a specific index in the given array. Here, index is an numerical value that indicates the location of array items. Thus, you can use this index to access elements of an array in Python.
An array is a container that holds a fix number of items of the same type. Python uses array module to achieve the functionality like an array.
Accessing array items in Python
You can use the following ways to access array items in Python −
Using indexing
Using iteration
Using enumerate() function
Using indexing
The process of accessing elements of an array through the index is known as Indexing. In this process, we simply need to pass the index number inside the index operator []. The index of an array in Python starts with 0 which means you can find its first element at index 0 and the last at one less than the length of given array.
Example
The following example shows how to access elements of an array using indexing.
import array as arr
# creating array
numericArray = arr.array('i',[111,211,311,411,511])#indexingprint(numericArray[0])print(numericArray[1])print(numericArray[2])
When you run the above code, it will show the following output −
111
211
311
Using iteration
In this approach, a block of code is executed repeatedely using loops such as for and while. It is used when you want to access array elements one by one.
Example
In the below code, we use the for loop to access all the elements of the specified array.
import array as arr
# creating array
numericArray = arr.array('i',[111,211,311,411,511])# iteration through for loopfor item in numericArray:print(item)
On executing the above code, it will display the following result −
111
211
311
411
511
Using enumerate() function
The enumerate() function can be used to access elements of an array. It accepts an array and an optional starting index as parameter values and returns the array items by iterating.
Example
In the below example, we will see how to use the enumerate() function to access array items.
import array as arr
# creating array
numericArray = arr.array('i',[111,211,311,411,511])# use of enumerate() functionfor loc, val inenumerate(numericArray):print(f"Index: {loc}, value: {val}")
In Python, to access a range of array items, you can use the slicing operation which is performed using index operator [] and colon (:).
This operation is implemented using multiple formats, which are listed below −
Use the [:index] format to access elements from beginning to desired range.
To access array items from end, use [:-index] format.
Use the [index:] format to access array items from specific index number till the end.
Use the [start index : end index] to slice the array elements within a range. You can also pass an optional argument after end index to determine the increment between each index.
Example
The following example demonstrates the slicing operation in Python.
Unlike other programming languages like C++ or Java, Python does not have built-in support for arrays. However, Python has several data types like lists and tuples (especially lists) that are often used as arrays but, items stored in these types of sequences need not be of the same type.
In addition, we can create and manipulate arrays the using the array module. Before proceeding further, let’s understand arrays in general.
What are arrays?
An array is a container which can hold a fix number of items and these items should be of the same type. Each item stored in an array is called an element and they can be of any type including integers, floats, strings, etc.
These elements are stored at contiguous memory location. Each location of an element in an array has a numerical index starting from 0. These indices are used to identify and access the elements.
Array Representation
Arrays are represented as a collection of multiple containers where each container stores one element. These containers are indexed from ‘0’ to ‘n-1’, where n is the size of that particular array.
Arrays can be declared in various ways in different languages. Below is an illustration −
As per the above illustration, following are the important points to be considered −
Index starts with 0.
Array length is 10 which means it can store 10 elements.
Each element can be accessed via its index. For example, we can fetch an element at index 6 as 9.
Creating Array in Python
To create an array in Python, import the array module and use its array() function. We can create an array of three basic types namely integer, float and Unicode characters using this function.
The array() function accepts typecode and initializer as a parameter value and returns an object of array class.
typecode − The typecode character used to speccify the type of elements in the array.
initializer − It is an optional value from which array is initialized. It must be a list, a bytes-like object, or iterable elements of the appropriate type.
Example
The following example shows how to create an array in Python using the array module.
import array as arr
# creating an array with integer type
a = arr.array('i',[1,2,3])print(type(a), a)# creating an array with char type
a = arr.array('u','BAT')print(type(a), a)# creating an array with float type
a = arr.array('d',[1.1,2.2,3.3])print(type(a), a)
Python array type is decided by a single character Typecode argument. The type codes and the intended data type of array is listed below −
typecode
Python data type
Byte size
‘b’
signed integer
1
‘B’
unsigned integer
1
‘u’
Unicode character
2
‘h’
signed integer
2
‘H’
unsigned integer
2
‘i’
signed integer
2
‘I’
unsigned integer
2
‘l’
signed integer
4
‘L’
unsigned integer
4
‘q’
signed integer
8
‘Q’
unsigned integer
8
‘f’
floating point
4
‘d’
floating point
8
Basic Operations on Python Arrays
Following are the basic operations supported by an array −
Traverse − Print all the array elements one by one.
Insertion − Adds an element at the given index.
Deletion − Deletes an element at the given index.
Search − Searches an element using the given index or by the value.
Update − Updates an element at the given index.
Accessing Array Element
We can access each element of an array using the index of the element.
Example
The below code shows how to access elements of an array.
from array import*
array1 = array('i',[10,20,30,40,50])print(array1[0])print(array1[2])
When we compile and execute the above program, it produces the following result −
10
30
Insertion Operation
In insertion operation, we insert one or more data elements into an array. Based on the requirement, a new element can be added at the beginning, end, or any given index of array.
Example
Here, we add a data element at the middle of the array using the python in-built insert() method.
from array import*
array1 = array('i',[10,20,30,40,50])
array1.insert(1,60)for x in array1:print(x)
When we compile and execute the above program, it produces the following result which shows the element is inserted at index position 1.
10
60
20
30
40
50
Deletion Operation
Deletion refers to removing an existing element from the array and re-organizing all elements of an array.
Here, we remove a data element at the middle of the array using the python in-built remove() method.
from array import*
array1 = array('i',[10,20,30,40,50])
array1.remove(40)for x in array1:print(x)
When we compile and execute the above program, it produces the following result which shows the element is removed form the array.
10
20
30
50
Search Operation
You can perform a search operation on an array to find an array element based on its value or its index.
Example
Here, we search a data element using the python in-built index() method −
from array import*
array1 = array('i',[10,20,30,40,50])print(array1.index(40))
When we compile and execute the above program, it will display the index of the searched element. If the value is not present in the array, it will return an error.
3
Update Operation
Update operation refers to updating an existing element from the array at a given index. Here, we simply reassign a new value to the desired index we want to update.
Example
In this example, we are updating the value of array element at index 2.
from array import*
array1 = array('i',[10,20,30,40,50])
array1[2]=80for x in array1:print(x)
On executing the above program, it produces the following result which shows the new value at the index position 2.
Python program to create a new dictionary by extracting the keys from a given dictionary.
d1 ={"one":11,"two":22,"three":33,"four":44,"five":55}
keys =['two','five']
d2={}for k in keys:
d2[k]=d1[k]print(d2)
It will produce the following output −
{'two': 22, 'five': 55} Dictionary Exercise 2 Python program to convert a dictionary to list of (k,v) tuples.
d1 = {"one":11, "two":22, "three":33, "four":44, "five":55} L1 = list(d1.items()) print (L1) It will produce the following output −
[('one', 11), ('two', 22), ('three', 33), ('four', 44), ('five', 55)] Dictionary Exercise 3 Python program to remove keys with same values in a dictionary.
d1 = {"one":"eleven", "2":2, "three":3, "11":"eleven", "four":44, "two":2} vals = list(d1.values())#all values uvals = [v for v in vals if vals.count(v)==1]#unique values d2 = {} for k,v in d1.items(): if v in uvals: d = {k:v} d2.update(d) print ("dict with unique value:",d2) It will produce the following output −
dict with unique value: {'three': 3, 'four': 44} Dictionary Exercise Programs Python program to sort list of dictionaries by values
Python program to extract dictionary with each key having non-numeric value from a given dictionary.
Python program to build a dictionary from list of two item (k,v) tuples.
Python program to merge two dictionary objects, using unpack operator.
